This application relates to optical fibers and fiber devices, and more particularly, to optical monitoring guided light in fibers.
Optical fibers can be used to transmit or process light in a variety of applications, including delivering light to or receiving light from integrated optical components or devices formed on substrates, transmitting information channels in wavelength-division multiplexed optical communication devices and systems, forming fiber optic switch matrix devices or fiber array to array connector, and producing optical gain for optical amplification or laser oscillation. Optical fibers essentially operate as xe2x80x9clight pipesxe2x80x9d to confine light within the fiber boundary and transfer light from one point to another.
A typical fiber may be simplified as a fiber core and a cladding layer surrounding the fiber core. The refractive Index of the fiber core is higher than that of the fiber cladding to confine the light. Light rays that are coupled into the fiber core within a maximum angle with respect to the axis of the fiber core are totally reflected at the interface of the fiber core and the cladding. This total internal reflection provides a mechanism to spatially confine the optical energy of the light rays in one or more selected fiber modes to guide the optical energy along the fiber core. Similarly, optical waveguides on substrates may also operate as light pipes to confine and transfer port light and may be used in integrated optical devices where optical elements, opto-electronic elements, or MEMS elements are integrated on one or more substrates.
The guided optical energy in the fiber or waveguide, however, is not completely confined within the core of the fiber or waveguide. In a fiber, for example, a portion of the optical energy can xe2x80x9cleakxe2x80x9d through the interface between the fiber core and the cladding via an evanescent field that essentially decays exponentially with the distance from the core-cladding interface. The distance for a decay in the electric field of the guided light is less than or on the order of one wavelength of the guided optical energy. This evanescent leakage may be used to couple optical energy into or out of the fiber core, or alternatively, to perturb the guided optical energy in the fiber core.
This application includes fiber tap monitors that detect or monitor guided light in a fiber or a planar waveguide by using an optical detector to receive a small amount of evanescent light obtained from a side-polished coupling port of the fiber or waveguide. The fiber or the planar waveguide is engaged to or formed on a substrate of a suitable material such as a semiconductor or glass.